The objective of this proposal is to understand the role of frascati, a novel mitochondrial solute transporter (SLC25), in vertebrate erythropoiesis and iron metabolism. Acquired and congential defects in iron metabolism from either deficiency or excess are one of the most common medical diseases. Mutations in the zebrafish frascati gene lead to a profound hypochromic anemia and a developmental arrest at the pro- erythroblast stage. Using a positional cloning strategy, we showed that frascati encodes a member of the mitochondrial solute carrier family. The frascati gene (mitoferrin, slc25a37) is highly expressed in fetal and adult hematopoietic tissues of zebrafish and mouse. We hypothesize that frascati is responsible for delivering iron to the mitochondria, and in particular, the mitochondria of developing erythroid cells. The goal of this application is to test this hypothesis. We propose to accomplish this goal by the following two specific aims: Specific Aim 1: Analysis of the biochemical function of the frascati gene. 1.1 The role of the frascati gene in mitochondrial iron acquisition will be studied using immortalized cells and zebrafish embryos deficient in frascati activity. 1.2 The physiologic substrate and transport properties of the frascati mitochondrial transporter will be studied by expression of recombinant protein as inclusion bodies in E. coli and their reconstitution in proteoliposomes. Specific Aim 2: Analysis of the frascati gene in mammalian organisms. 2.1 The function of the frascati gene in mouse will be studied by targeted gene disruption. Insight into the function of the frascati gene will be directly relevant to our understanding of human disorders of iron deficiency anemia and iron-overload.